Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$201.45	6.164%	$213.8674	$213.87	$213.85	$213.90
Purchase #2	$138.46	5.847%	$146.5558	$146.56	$146.55	$146.60
Purchase #3	$173.65	13.421%	$196.9556	$196.96	$196.95	$197.00
Purchase #4	$28.61	11.253%	$31.8295	$31.83	$31.85	$31.80
Purchase #5	$98.28	13.672%	$111.7168	$111.72	$111.70	$111.70
Purchase #6	$29.34	4.581%	$30.6841	$30.68	$30.70	$30.70
Purchase #7	$10.40	13.802%	$11.8354	$11.84	$11.85	$11.80
7 purchase totals =	$680.19		$743.4446	$743.46	$743.45	$743.50